DESCRIPTION The general aim of this project is to study the molecular mechanisms involved in axial patterning of the early vertebrate embryo. This study is based on the premise that molecular and morphogenetic interactions which occur during gastrulation serve to establish the definitive axis of the embryo. Furthermore, this study makes the assumption that it is primarily through the activities associated with a specific region of the gastrula stage embryo, known as the organizer in amphibians, which establish the global organization of the early embryo's body plan. Thus, in studying the regulation of genes expressed in the early gastrula organizer, one can generate a method for the establishment of the organizer, and therefore by extension, the overall patterning of the embryo. The specific objectives of the proposed research plan involve the study of the regulation of the goosecoid (gsc) gene in response to activin and other TGFbeta superfamily members, and includes: (1) A characterization of the nature of 6the interaction of an activin response element binding protein which has been recently identified (see below), with its target sequence in the gas promoter; (2) An analysis of the interaction of the activin response element binding protein with smad3.